Neuromuscular fatigue after maximal stretch-shortening cycle exercise.
To examine some possible sites of fatigue during short-lasting maximally intensive stretch-shortening cycle exercise, drop jumps on an inclined sledge apparatus were analyzed. Twelve healthy volunteers performed jumps until they were unable to maintain jumping height > 90% of their maximum. After the workout, the increases in the blood lactate concentration and serum creatine kinase activation were statistically significant (P < 0.001 and P < 0.05, respectively) but rather small in physiological terms. The major changes after the workout were as follows: the single twitch was characterized by smaller peak torque (P < 0.05) and shorter time to peak (P < 0.05) and half-relaxation time (P < 0.01). The double-twitch torque remained at the same level (P > 0.05), but with a steeper maximal slope of torque rise (P < 0.05); during 20- and 100-Hz stimulation the torque declined (both P < 0.01) and the maximal voluntary torque changed nonsignificantly but with a smaller maximal slope of torque rise (P < 0.01) and a higher activation level (P < 0.05), accompanied by an increased electromyogram amplitude. These findings indicate that the muscle response after the short-lasting consecutive maximum jumps on the sledge apparatus may involve two distinct mechanisms acting in opposite directions: 1) The contractile mechanism seems to be potentiated through a shorter Ca2+ transient and faster cross-bridge cycling, as implied by twitch changes. 2) High-frequency action potential propagation shows an impairment, which is suggested as the possible dominant reason for fatigue in exercise of this type.
Strojnik
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Department of Biology of Physical Activity, University of Jyuskyl, Finland.
Komi
P V
PV
D000200:Action Potentials / Q000502:physiology; D000328:Adult; D001642:Bicycling / Q000502:physiology*; D004558:Electric Stimulation; D004576:Electromyography; D015444:Exercise / Q000502:physiology*; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D007717:Knee / Q000502:physiology; D008297:Male; D018763:Muscle Fatigue / Q000502:physiology*; D012026:Reflex, Stretch / Q000502:physiology